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The attentional blink (AB) phenomenon occurs when perceivers must report two targets embedded in a sequence of distracters; if the first target precedes the second by 200–600 msec, the second one is often missed. We investigated AB by measuring dynamic cross-lag phase synchronization for 565 electrode pairs in 40-Hz–range EEG. Phase synchrony, on average, was higher in experimental conditions, where two targets are reported, than in control conditions, where only the second target is reported. The effect occurred in electrode pairs covering the whole head. Timing of the synchrony was crucial: Brief episodes of enhanced synchrony occurred 100–500 msec before expected target onset in AB conditions where the second target was correctly reported. These results show that intrinsic brain dynamics produce anticipatory synchronization in transient assemblies of cortical areas. Enhanced levels of anticipatory synchronization occur in response to the demands of the task in conditions where the system's limited capacity is under strain. [ABSTRACT FROM AUTHOR]

Abstract: Objective: Data from a previous event-related potential (ERP) study in visual-perceptual grouping [Nikolaev AR, van Leeuwen C. Flexibility in spatial and non-spatial feature grouping: an event-related potentials study. Brain Res Cogn Brain Res 2004;22:13–25] were re-analyzed to identify event-related dynamics of phase-synchronization. Methods: In 20Hz activity, uniform spreading of phase synchronization in closely spaced (∼2cm) scalp electrodes appears and disappears spontaneously. The lengths of synchronized activity intervals and how they vary as a function of stimulus presentation were compared between task and control conditions. Results: Synchronization reached a maximum in the task condition about 180ms post-stimulus onset, coinciding with the peak N180 ERP marking the deployment of task-specific attention. Synchronized intervals were longer in the task than in the control condition. Long (above 80ms) intervals occurred at a stable rate before and just after stimulus onset, but steeply decreased 200–400ms afterwards. Conclusions: Perceptual tasks lead to longer synchronized intervals in early visual areas. Attention deployment resets the ongoing synchronization. Event-related activity, besides low-frequency ERP, consists of high-frequency short and long synchronized intervals corresponding to evoked bursts and ongoing oscillations, respectively. Significance: High-density scalp recorded EEG revealed synchronization dynamics in a local, early visual area of cortex that can be interpreted as modulation of spontaneous ongoing task-related processes by attention. [Copyright &y& Elsevier]

Abstract: In a visual task using 12 healthy subjects, spread of evoked phase-synchronized activity was studied in local cortical areas. The areas were identified in a previous study of the same data set using event-related potentials (ERP). Chains of closely spaced (∼2 cm) scalp electrodes covering these areas were selected for phase synchronization analysis in which task and control conditions were compared. Phase synchronization spreading in the task condition at 20 Hz reached a maximum about 180 ms post-stimulus in the right occipital area. This maximum coincides with the attention-related negative peak N180 in the corresponding ERP study. Intervals of evoked phase synchronization were longer in the task than in control condition. It was concluded that attention-related modulation of evoked activity is reflected not only in enhanced amplitude of low-frequency ERP, but also in phase synchronization of high-frequency ongoing rhythms in local brain areas. [Copyright &y& Elsevier]

Spatiotemporal characteristics of spontaneous alpha EEG activity patterns are analyzed in terms of large-scale phase synchronization. During periods with strong phase synchronization over the entire scalp, phase patterns take either of two forms; one is a gradual phase shift between frontal and occipital regions and the other is a stepwise pattern with a sudden phase shift in the central region. The former is regarded as a traveling wave of electrocortical activity, of which the direction of propagation is predominantly from anterior to posterior in three out of four subjects, and opposite in the remaining one. The other activity pattern observed may correspond to a standing wave composed of two traveling waves propagating in opposite directions. The duration distributions of these patterns have similar forms within a subject, which suggests that they share the same mechanism for their generation. [ABSTRACT FROM AUTHOR]

The dynamical properties of large-scale, long-term phase synchronization behavior in the alpha range of electroencephalographic signals were investigated. We observed dynamical phase synchronization and presented evidence of an underlying spatiotemporal ordering. Fluctuations in the duration of episodes of intermittent synchrony are scale-invariant. Moreover, the exponent used to describe this behavior is stable across different normal subjects. The results provide a new feature of self-organization in human brain activity and constitute a quantitative basis for modeling its dynamics. [Copyright &y& Elsevier]